What did the partition contain? Where was it mounted? Also, did you recently switch it from ext3 to ext4? There are some changes in ext4 that will make it read-only to computers without ext4 support
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HuckleOct 2 '12 at 20:47

It contains the operating system and the data, it was the "/" mount point. It was ext4, it was just resized.
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userOct 2 '12 at 20:52

1 Answer
1

Something is wrong with the metadata for the chromium cache file. It might not hurt to delete the cache files, but fsck with the -f flag (force) should fix this issue either way. (clarification per IR: run fsck from the livecd, since it needs to be run on an unmounted partition)

$ sudo fsck.ext4 -f /dev/sda1

If you need to remount the disk in read/write mode, try this:

$ sudo mount -vo remount,rw /

Edit: This seems to be part of a larger, unresolved issue with Ext4. Other people have experienced the same problem after resizing or copying partitions (and sometimes without doing either).

fsck should only be run on an unmounted partition - at that point it is neither read-only nor read-write.
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ImaginaryRobotsOct 5 '12 at 15:38

I've deleted the chromium chache, but fsck said /dev/sda1 was clean before and after the delete operation. (That's why I was looking for some other way to check the readability of the files. So I could make sure that there are not other wrong files like this.)
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userOct 5 '12 at 16:02

Did you run fsck with the -f option? At the bottom of the launchpad link, someone with the same problem deleted the chromium cache file and the situation seems to have resolved. This may be part of a larger issue with ext4.
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Mark LoiseauOct 5 '12 at 17:57

Yes, I ran it with -f option, and I think GParted passes the -t option to e2fsck when checking, too. However I haven't got this error since I deleted the cache.
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userOct 9 '12 at 0:26